What is a theatrical trailer?

I think that the idea of a theatrical trailer is very successful because it makes the film known about and so audiences can acknowledge that they may want to go and see the movie. With the release dates being visible the target audience can then arrange to go and watch it. A theatrical trailer will target its target audience as well as widen it because it will tell more of the story and so the audience are allowed to know more about it and decide wether or not they may want to go and watch the film.
I find that the titles on the trailer allows an audience member to acknowledge that I will want to see it. However, a theatrical trailer mustn't reveal too much of the story-line because otherwise the drama and twists will be ruined and so the audience may feel as if they have already seen the film and so wouldn't want to go and watch it in the cinema. Therefore film companies should be very clever with the shots and scenes that they present within their theatrical trailers because they want to make sure they are steal capturing the audiences attention and anticipation.